Re: [HACKERS] asynchronous execution

Hello. This is the final report in this CF period.

At Fri, 17 Mar 2017 17:35:05 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in
<20170317.173505.152063931.horiguchi.kyotaro@lab.ntt.co.jp>
> Async-capable plan is generated in planner. An Append contains at
> least one async-capable child becomes async-aware Append. So the
> async feature should be effective also for the UNION ALL case.
> 
> The following will work faster than unpatched version.I 
> 
> SELECT sum(a) FROM (SELECT a FROM ft10 UNION ALL SELECT a FROM ft20 UNION ALL SELECT a FROM ft30 UNION ALL SELECT a
FROMft40) as ft;
 
> 
> I'll measure the performance for the case next week.

I found that the following query works as the same as partitioned
table.

SELECT sum(a) FROM (SELECT a FROM ft10 UNION ALL SELECT a FROM ft20 UNION ALL SELECT a FROM ft30 UNION ALL SELECT a
FROMft40 UNION ALL *SELECT a FROM ONLY pf0*) as ft;
 

So, the difference comes from the additional async-uncapable
child (faster if contains any). In both cases, Append node runs
children asynchronously but slightly differently when all
async-capable children are busy.

I'll continue working on this from this point aiming to the next
commit fest.

Thank you for valuable feedback.

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center